Omnidirectional vent cap

ABSTRACT

An omnidirectional vent cap for venting holding tanks is provided. Current vent caps seldom exhaust gasses and create higher rather than lower pressure above the vent. By providing a 360 degree channel, the present invention can use a small movement of air to significantly reduce the air pressure above the exhaust port to draw out vapors. Since the device is symmetrical about the central axis the movement of air can be from any direction relative to the device.

TECHNICAL FIELD

The application relates to the field of ventilating caps for ventilating exhaust vents, such as roof top vents for recreational vehicle holding tanks and the like.

BACKGROUND

Ventilator caps are widely used to facilitate venting from gas exhaust outlets on building roofs and transportation vehicles. For example, recreational vehicles utilize a holding tank for storage and processing of sewage (black water) and/or grey water. Such holding tanks are generally vented to the exterior atmosphere by a vent pipe which typically exits the vehicle through the roof of the vehicle. A cap is provided on the vent pipe to prevent objects from entering the pipe. However, the unpleasant odors can accumulate in the holding tank and seep back into the living area of the vehicle.

To improve and facilitate the exhaust of gases from the holding tank, a rotating vent cap resembling a wind vanes has been used to take advantage of wind movement. Such vent caps are pivotally connected to the outlet of the vent pipe and have a vane which causes the outlet opening to point downwind, thereby drawing vapors from the holding tank. A drawback of such vent caps however is that they require a certain minimum wind velocity to function effectively, in particular at least enough wind velocity to pivot the wind vane. In the absence of that minimum wind force, the device may not function.

Other venting apparatus are shown in U.S. Pat. No. 55,094 Hardy; U.S. Pat. No. 3,302,552 Walsh; U.S. Pat. No. 3,347,147 and U.S. Pat. No. 3,382,792 Howard; U.S. Pat. No. 3,509,811 Topp; U.S. Pat. No. 4,531,455 Palmer; and U.S. Pat. No. 4,603,619 Amphoux.

It is therefore desired to provide a vent cap which functions to improve the exhaust of gasses from holding tanks or the like omni-directionally with no moving parts and with a minimum of air movement.

SUMMARY OF INVENTION

An omnidirectional vent cap for venting holding tanks is provided. The invention provides a roof vent cap for venting an exhaust gas passage, comprising: i) a generally circular base having a central opening for communicating with the exhaust gas passage and a generally circular perimeter, and an upper ramp surface extending between the perimeter and the central opening, the ramp surface having an increasing slope as the distance from the central opening decreases; ii) a top cover element supported above the base and having an outer edge and providing a convex lower surface extending at its lowest point below the outer edge to thereby in combination with the base cause a effect above the exhaust gas passage when air moves through the cap; and iii) means for supporting the top cover element above said base. According to one aspect the invention further comprises a plurality of spaced, radially extending vanes projecting upwardly from the upper ramp surface. By providing a 360 degree channel, the present invention can use a small movement of air to significantly reduce the air pressure above exhaust port to draw vapors from the exhaust pipe. Since the device is symmetrical about the central axis the movement of air can be from any direction relative to the device.

BRIEF DESCRIPTION OF DRAWINGS

In drawings which illustrate a preferred embodiment of the invention:

FIG. 1 is a perspective view of the vent cap of the invention:

FIG. 2 is a front elevation view of the vent cap shown in FIG. 1 having a variation in the shape of the support legs;

FIG. 3 is a detail view in front elevation of the base of the vent cap shown in FIG. 2;

FIG. 4 is a top view of the base shown in FIG. 3;

FIG. 5 is a cross-section of the cap taken along lines 5-5 of FIG. 6;

FIG. 6 is a top view of the vent cap shown in FIG. 1;

FIG. 7 is a cross-section view showing a recreational vehicle holding tank;

FIG. 8 is a perspective view showing the installation of the vent cap shown in FIG. 2; and

FIG. 9 is a front elevation view of the vent cap shown in FIG. 1 having a further variation in the shape of the support legs.

DESCRIPTION

Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

FIG. 7 illustrates a holding tank 10, containing sewage 14, and having an air inlet 16 and a vent pipe 18 extending through roof 20. The vent cap 22 of the invention is shown in FIG. 1. It has a base 24, top 26 and support legs 28 joining the base 24 and top 26. It is preferably formed of molded plastic but could be constructed of other synthetic or natural materials including wood and metal or combinations of such materials.

Top 26, as shown in FIG. 6, serves as a cap to prevent materials from entering vent pipe 18. It has a convex or domed upper surface 30 which provides an aerodynamic shape and permits water and debris to run off. Top 26 has a convex lower surface 32 which forms the upper surface of the channel formed between base 24 and top 26. The central area or apex 33 of convex lower surface 32 (see FIG. 5) extends below the outer edge 31 of upper surface 30 by a distance A. Legs 28, whose number and thickness are preferably minimized to reduce air turbulence and whose shape is similarly chosen to reduce air turbulence, support top 26 at the appropriate height above base 24. It has been found that a useful minimum separation of base 24 from top 26 is about ½ the length of the ramp surface 40 as described below.

Base 24, as shown in FIG. 1-4, is circular in top view and has a central cylindrical opening 34 for receiving the vent pipe 18, as shown in dotted outline in FIG. 3. The bottom surface 36 of base 24 is flat. The circular outer circumference of base 24 forms a generally vertical rim or edge 38. A radially extending ramp 40 is formed on the upper surface of base 24 between the outer edge 38 and central opening 34. The surface of ramp 40 is curved, with a smoothly increasing tangential angle, being almost flat at edge 38 to about 80 degrees at opening 34. The vertical height of the ramp rises about one-half its surface distance over the curvature of the ramp from outer to inner edge. The radial length of the ramp is preferably roughly the same as the radius of opening 34. The shape of ramp 40 causes the moving air to be accelerated upwardly away from the exhaust port 34. The shape of ramp 34, in combination with the shape of surface 32, causes a low pressure effect above exhaust port 34 causing the vapors to be drawn upwardly from holding tank 10.

To further improve the operation of the device, radial channeling vanes 48 which extend vertically from ramp 40 may be provided. Vanes 48 serve to focus and direct the air flow toward the center of the device, and reducing the amount of air that slips around the side of the raised inner area of the device. Due to the radial direction of the vanes, the space between vanes decreases towards the center of the device, thereby funneling, concentrating and magnifying the air flow as it reaches the center of the device, and further increasing the air speed and lowering the air pressure above exhaust port 34. The height of the vanes 48 above ramp 40 is preferably 5% to 10% of the length of the surface of ramp 40.

In this way a small movement of air can be channeled by the vent cap 22 to significantly reduce the air pressure above exhaust port 34 to draw vapors from holding tank 10 even with light air movement from any direction. Since the device is symmetrical about the central axis the movement of air can be from any direction relative to the device.

While the device has been described in the context of a vent cap for a holding tank, it will be apparent to the person skilled in the art that the present invention will have application in other venting applications also including chimneys, other types of roof vents, and other transportation vehicles.

As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims. 

1. A vent cap for venting an exhaust gas passage, comprising: i) a generally circular base having a central opening for communicating with said exhaust gas passage and a generally circular perimeter, and an upper ramp surface extending between said perimeter and said central opening, said ramp surface having an increasing slope as the distance from the central opening decreases; ii) a top cover element supported above said base and having an outer edge and providing a convex lower surface extending at its lowest point below said outer edge to thereby in combination with said base cause a low pressure effect above said exhaust gas passage when air moves through said cap; and iii) means for supporting said top cover element above said base.
 2. The vent cap of claim 1 further comprising a plurality of spaced, radially extending vanes projecting upwardly from said upper ramp surface.
 3. The vent cap of claim 2 wherein said vanes extend above said ramp surface a distance which is 5% to 10% of the length of said ramp surface.
 4. The vent cap of claim 1 wherein said top cover element comprises a convex upper surface.
 5. The vent cap of claim 1 wherein said top cover element and said base have a minimum separation of approximately ½ the length of said ramp surface.
 5. The vent cap of claim 1 wherein said ramp surface is curved with a smoothly increasing tangential angle
 6. The vent cap of claim 1 wherein said ramp surface is approximately horizontal at its outer edge and is about 80 degrees at the central opening.
 7. The vent cap of claim 1 wherein said ramp surface rises about one-half its surface distance over the curvature of the ramp from outer to inner edge.
 8. The vent cap of claim 1 wherein the radial length of said ramp surface is approximately the same as the radius of said central opening.
 9. The vent cap of claim 1 wherein said means for supporting said top cover element above said base comprise a plurality of legs.
 10. A vent cap for venting an exhaust gas passage, comprising: i) a generally circular base having a central opening for communicating with said exhaust gas passage and a generally circular perimeter, and an upper ramp surface extending between said perimeter and said central opening, said ramp surface having an increasing slope as the distance from the central opening decreases; ii) a top cover element supported above said base and having an outer edge and providing a convex lower surface extending at its lowest point below said outer edge to thereby in combination with said base cause a low pressure effect above said exhaust gas passage when air moves through said cap; iii) means for supporting said top cover element above said base; and iv) a plurality of spaced, radially extending vanes projecting upwardly from said upper ramp surface.
 11. The vent cap of claim 10 wherein said vanes extend above said ramp surface a distance which is 5% to 10% of the length of said ramp surface.
 12. The vent cap of claim 10 wherein said top cover element comprises a convex upper surface.
 13. The vent cap of claim 10 wherein said top cover element and said base have a minimum separation of approximately ½ the length of said ramp surface.
 14. The vent cap of claim 10 wherein said ramp surface is curved with a smoothly increasing tangential angle
 15. The vent cap of claim 10 wherein said ramp surface is approximately horizontal at its outer edge and is about 80 degrees at the central opening.
 16. The vent cap of claim 10 wherein said ramp surface rises about one-half its surface distance over the curvature of the ramp from outer to inner edge.
 17. The vent cap of claim 10 wherein the radial length of said ramp surface is approximately the same as the radius of said central opening.
 18. The vent cap of claim 10 wherein said means for supporting said top cover element above said base comprise a plurality of legs. 